1. Technical Field
The present invention relates to internal combustion engine control systems and in particular starting systems for diesel engines.
2. Background to the Invention
An internal combustion engine is routinely cranked for starting. Cranking of the engine continues until the cylinders of the engine begin firing and the engine begins generating sufficient power fully to compress the fuel/air mixture being injected into the cylinders for ignition. In the case of diesel engines, a starter system includes an electric motor of sufficient output to turn an engine crankshaft and to force pistons far enough into cylinders to compress the air/fuel mixture and thereby raise the mixture to its ignition temperature. The electric starter motor typically draws power from a vehicle battery, although other sources may be used. The electrical starter motor drives a pinion gear, which in turn engages a fly wheel ring gear coupled to the engine""s crankshaft to crank a motor. A solenoid controls engagement of the pinion with the ring gear by moving the pinion into and out of contact with the ring gear. To prevent damage to the starter motor, excessive wear on the pinion and an unneeded load on the engine during normal operation, the solenoid operates to control positioning of the pinion relative to the ring gear.
Diesel engines rely on compression of the fuel/air mixture to raise the air/fuel mixture temperature to its flash point and can be difficult to start. Due to this factor, among other causes, truck drivers often make several attempts to start a diesel engine. An attempt to start an engine may end with a piston fully or partially inserted into a cylinder and a compressed air/fuel mixture in the cylinder which acts a spring forcing the piston out of the cylinder. In this situation the piston can turn the engine crankshaft in a direction counter to the cranking direction, a phenomena called rock back. If an attempt is made to reengage the pinion with the ring gear, a substantial possibility exists that the pinion will be damaged or stripped.
Accordingly it is preferable that rotation of an engine completely stop before a follow-up attempt to start the engine is made. One technique to achieve this, known to the art, is to force a vehicle operator to fully reset the ignition key to the off position between start attempts. The time taken to do this act is usually sufficient to allow the engine to complete any rock back. Many trucks however have a starter button, rather than, or in addition to, a start position for the ignition key. Such buttons, or ignition keys could be monitored by addition of a monitoring switch which would have to be reset. All such systems involve the additional expense of buying and incorporating such a switch into an engine starting system.
Engine crank inhibit circuitry has been used with trucks built by the Assignee of this Patent to block attempts to crank an engine which is already running. An electronic engine control module (EECM) provides an inhibit signal which prevents cranking by deenergizing a start relay. The EECM has no hardwire connection to either the ignition switch or to a start button and develops the inhibit signal without reference to the position of the ignition switch.
U.S. Pat. No. 4,916,327 to Cummins proposes a pinion block and rock-back protection circuit. Briefly, the ""327 circuit provides a capacitive discharge circuit, described from column 18, line 66 to column 19, line 35, which prevents reengaging the starter motor before its complete discharge. This prevents the ignition switch from engaging the starter motor after an excessively quick cycle, which is typically set at 2 seconds, but which can be adjusted. Dedicated circuit elements are used to implement this system.
The invention provides a control system for an electric starter to an internal combustion engine. Typically, the engine is mounted on a vehicle and is connected by a transmission to a drive shaft. The control system includes a starter switch which electrically connects a cranking motor to a source of electrical power. The engine has a crank shaft ring gear which is open to be engaged. A pinion rotationally driven by the cranking motor is pushed into engagement with the crank shaft ring gear while the cranking motor is turning. An indication of engine rotational speed is developed from the signal produced by a cam shaft position sensor, which functions as a tachometer. Control logic is provided which is responsive the engine rotational speed signal for developing indications of engine deceleration indicative of cessation of cranking and for generating an engine crank inhibit signal having a state reflecting cessation of cranking.
The control logic further comprises a delay line connected to the cam position sensor to receive the engine rotational speed signal and responsive thereto for producing a delayed engine rotational signal. A summing element connected to receive the engine rotational speed signal and the delayed engine rotational speed signal produces a difference signal corresponding to engine acceleration or deceleration. A comparator takes the difference signal and the difference threshold reference signal as inputs and responsive thereto generates a minimum speed change indication signal of one of two states, where a first state indicates a change in engine rotational velocity consistent with cessation of engine cranking and the second state indicating otherwise.
The control logic still further includes a source of an engine speed reference signal, a comparator taking the engine speed reference signal and the engine speed signal as inputs to produce a minimum engine speed signal of one of two states, where a first state indicates that engine speed falls below a minimum threshold and a second state which indicates that engine speed exceeds a minimum threshold. A logical AND gate taking the minimum speed signal and the minimum speed change indication signal as inputs to provide an cranking inhibit set signal when both inputs go high.
Additional effects, features and advantages will be apparent in the written description that follows.